The pH of the nutrient solution is a major determinant of nutrient uptake by the plant. If the pH wanders outside the optimum range of between pH 5.1 and pH 5.9, then nutritional deficiency and/or toxicity problems can occur. For hydroponic nutrient solutions used with inert media, keep the pH at 5.2 for optimal elemental uptake. It is at this point that roots most readily assimilate nutrients. These pH and TDS/EC recommendations may seem low relative to the normally suggested range, but are based upon information garnered from "Hydroponic Nutrients" by M. Edward Muckle and Practical Hydroponics and Greenhouses. They both document the low pH resulting in increased nutrient uptake and my experience has shown discernible health and yield improvements at a ph of 5.2 over higher levels.

On page 100, Hydroponic Nutrients displays both the assimilation chart for organic soil applications and another for inert medium hydroponics, which depicts the vastly different scenarios (see below). The widely accepted soil based chart is frequently misapplied to water culture applications. His research and that done by others, documented in Practical Hydroponics and Greenhouses, indicate that iron and phosphorous precipitate in nutrient solutions at pH levels above 6. Stay below a pH of 6 by all means to avoid this problem and benefit.

The nutrient assimilation rate is further enhanced by the reduction in solution TDS/EC, which reduces osmotic pressure and allows the roots to draw the nutrients "easier". Young, established seedlings or rooted cuttings are started at 500-600ppm. The TDS is increased to 800-900ppm during peak vegetative growth. During the transition from early to heavy flowering, TDS is further raised to 1000ppm. It is then reduced to 400-500ppm during the final 2 weeks of flushing. The plants demonstrate their preference for a lower TDS/EC when running a lower pH by clearly sustaining higher growth rates.

The optimum temperature for hydroponic solutions to be is 24c/75f. At this point, most elements are assimilated highest and atmospheric oxygen is most readily dissolved. Although increases in temperature increase the rate of photosynthesis, avoid exceeding the maximum listed of 25c/78f. Elevated temperatures make some elements more available, but reduce the solution's dissolved oxygen capacity, increasing root disease likelihood.

I found these numbers a while back on the internet, but so far, they have been right on each time my PH has been off. I was at 6.0-6.1 PH for a few days and I started to get uniform, light yellow leaves, and burnt edges around the sides of my leaves. Just as this chart says, at that PH, Potassium (K) and Zinc (Zn) are locked out and the symptoms are of those two being locked out. That was only one of the many times list list has been correct and helped me out, so I'm a true believer in the list above.

Plus at 5.2, your almost locking out Nitrogen and thats the last nute you want to be locking out or even coming close to locking out.

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

MM where are you getting your information? I really don't think you can generalize these conditions. A lot of nutes list a target ph. For example, the Ionic line claims that the hydro target ph range for their nutes is 5.8-6.2. Fox Farm recommends 5.8-6.3. Most experts agree that hydroponic solutions should maintain a ph level between 5.5-6.5. I am not sure about this 5.2. Maybe the best advice would be to suggest that everyone follow very closely the instructions for their nutes, at least until they have experience with the nutes/strain. Best wishes.

I found these numbers a while back on the internet, but so far, they have been right on each time my PH has been off. I was at 6.0-6.1 PH for a few days and I started to get uniform, light yellow leaves, and burnt edges around the sides of my leaves. Just as this chart says, at that PH, Potassium (K) and Zinc (Zn) are locked out and the symptoms are of those two being locked out. That was only one of the many times list list has been correct and helped me out, so I'm a true believer in the list above.

Plus at 5.2, your almost locking out Nitrogen and thats the last nute you want to be locking out or even coming close to locking out.

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

Also, 75 degrees is not the optimum temp for the solution as this is the highest temp the res should ever reach. Above 75 degrees runs the risk of pythium. The temp range is actually 65-75 degrees, with 68 degrees reported to be the best temp for oxygen (not co2) uptake at the roots. Ya dig?

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

This advice, while well and clearly written, is definitely bullshit. I've been growing cannabis hydroponically since the mid-1980's and have found the following to be true in EVERY case. I largely use General Hydroponics Flora series, though I have also used Fox Farm and Advanced Nutrients

TDS Sweetspot
This varies according to where in the cycle you are. Suffice to say I follow this regimen:

Clones: 200-400ppm AFTER roots appear (nothing before that)
Veggie: 800 or so, although can go aggressive and boost to 1000 once the plant is well established.
Bloom: 1000 or so for the first couple weeks, then boost up to 1200 for almost any strain. Some strains (old NL#5, etc.) can take up to 1800 if you've got enough light intensity (over 55W per square foot) and CO2 (1100-1500ppm) to ensure the plant can uptake the nutrients.

If I had the space to setup separate systems for research into this issue, I would do so, but on the surface, this is bullshit unless there are other factors involved that would raise the actual nutrient Ph at the rootzone.

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

Great info.

Lets say I am a first time grower, which I am. If I walk into a nursery and go looking for hydroponic nutrients what levels of N-P-K do I need to purchase? I need to know which time frames for each level of N-P-K. Weeks 1-3 gets ____, 4-6 gets ____, ect. Mind you I'm not real sure if we have any Nursuries devoted directly to hydro, any tips on what to ask and what to look for?

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

thats cool but what I need to really know is should I start of with a 10-20-10 then move to a 25-10-10 mix or what. Basically when I go to buy the nutrients what are the NPK formulas do I need to get? And of course what is the time frame of use for each solution?

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

Originally Posted by Roman

thats cool but what I need to really know is should I start of with a 10-20-10 then move to a 25-10-10 mix or what. Basically when I go to buy the nutrients what are the NPK formulas do I need to get? And of course what is the time frame of use for each solution?

If I were you, I'd just buy a 2 or 3 part Hydro nute offline and follow the directions on the bottle. If your a first time grower, trying to mix and match nutes, your failure rate goes up through the roof. Just stick with something simple like a General Hydro two or three part nute system.

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

Re: What levels should I maintain for my hydroponic nutrient, temperature, pH and TDS

Hello Kind People,

I am currently researching system design and have a few questions if you please, as I am rather curious as I have read the thread information and found it to be fascinating.

It is very interesting how so many instructions may differ due to system specification variation.

With a deep flood and drain pod system (rock-wool cubes/clay pebbles) which is programed to flood & drain every 3 hours (24/7)
Is it correct that a PH of 6.0 @ 20 Degrees C is required ?

Is it also correct the systems reservoir should also be maintained @ 20 Degrees C and incorporate an air supply/airstone ring to ensure a stable PH ?

If each of the systems pod buckets had a "Turbo" aeration ring in the bottom under the clay pebbles, should the compressed air temp supplied to the "Turbo" aeration ring for the roots be at approx 22-24 Degrees C.